The invention relates to a lay-up head fitted with a device for separating prepreg from its backing tape.
It is known practice to automatically deposit on a mold or depositing tool, by virtue of a robot furnished with a lay-up head, a tape or a layer of fibers for the manufacture of various parts such as aircraft wings, from a composite tape consisting of fiber elements (carbon, glass, Kevlar®, etc.) that are bonded, by impregnation of a thermoplastic or heat-curable resin, and supported on a backing tape made of paper or of plastic film. The prepreg is made to pass beneath a depositing member of the lay-up head and is deposited on the mold or the tool by virtue of said depositing member, which may be, for example, a roller which if necessary is segmented.
U.S. Pat. No. 5,314,563 teaches of such methods for depositing composite by means of a lay-up head, in which the prepreg is brought up to the depositing member of the lay-up head on its backing tape, is deposited by virtue of a depositing member, the backing tape itself passing beneath the depositing member and then being rewound downstream of the depositing member.
Since such methods have drawbacks, the Applicant has produced and described in U.S. Pat. No. 4,842,684 a method in which the composite tape is paid out from a reel in order to pass over the lay-up head where the tape of prepreg fibers is separated from the backing tape. The backing tape is returned to a winding mandrel, while the prepreg is applied to the mold or the previous layers already deposited, by a depositing and compacting member usually consisting of a roller or an applicator shoe connected to the lay-up head. Unlike the methods of the prior art, the backing tape is separated from the prepreg just upstream of the depositing member.
Because of the shapes of the parts made, and notably the edges thereof, it is advisable not only to deposit “full width” sections of tape, with four sides, but also sections of various shapes obtained by complex cutting of the tape.
For through-cuts of simple shapes, a single-phase depositing process is used which comprises the cutting in situ of the strips to be deposited and their being immediately deposited by the same machine. A mechanical or ultrasound knife cuts the prepreg tape directly on its backing paper without cutting the latter which will be rewound onto the mandrel after peeling just upstream of the depositing member.
For strips to be cut of complex shape, the Applicant has produced a two-phase method according to which the cut is made upstream of the depositing method itself, with a first specialized machine in which the successive sections that are precut are deposited on the initial or repackaged backing tape between two protectors and wound onto a cassette subsequently installed on the lay-up head.
In order to provide the best possible guidance of the prepreg, the prepreg and its backing must be separated as close as possible to the depositing roller of the lay-up head, placed across the tape.
However, this requirement is difficult to meet when the successive cuts of the prepreg are placed on the backing tape in a manner that leads to seeing, side by side in one and the same transverse line of the tape, portions of two successive sections: this is the case notably when there is an oblique cut, for example at 45°, between two sections, where the tail of the first section is next to the head of the second section. In order to prevent the head of the second section passing beneath the depositing roller while the first section is not yet fully deposited, it is then necessary to maintain the distance between said roller and the separator at a distance greater than the overlap length of the two successive sections, that is to say greater than the width of the tape in the case of a 45° cut where the overlap length is equal to the width of the tape. This necessary distance is therefore greater than would be desirable if it were not made essential because of the oblique cut, and notably in the normal case of a simple crosswise cut. The result of this is a risk of incorrect guidance of the prepreg tape.
In order to remedy this problem, the Applicant has described, in French Publication FR 2 888 156, a lay-up head of a prepreg tape in which a prepreg tape juxtaposed to a backing tape is separated from its backing tape by peeling by means of a separator just upstream of a member for depositing the prepreg tape on a depositing tool, and in which the distance between the separator and the depositing member is adjustable by virtue, for example, of a movable carriage. This distance is adjustable during deposition between a minimum value in which the separator and the depositing member are very close to one another and a maximum value in which they are separated by a distance at least equal to the width of the tape (for a 45° cut), in order to allow the separation of the backing in the case of successive sections separated by an oblique cut.
This device gives perfect satisfaction, but requires a certain space to obtain the rigidity that is compatible with the requirements of depositing precision.